This invention relates to a recording and playback apparatus such as a digital video tape recorder (hereinafter, `video tape recorder` will be abbreviated to `VTR`) or a digital audio tape (hereinafter abbreviated to `DAT`) recorder, and particularly to an apparatus and method in which a PLL (Phase-Locked Loop) generating a clock synchronized with data played back from a magnetic tape is so controlled that it operates stably even when the magnetic tape is being transported at a high speed.
Digital VTRs for recording and playing back a compressed and encoded video signal on a magnetic tape together with an encoded audio signal (as described in for example `Illustrated Digital Video Reader`, Yukio Kubota Ed., Ohm Co., Ltd., Aug. 25, 1996) are known. In a digital VTR, a subcode is recorded together with the video signal and the audio signal, and the format of this subcode has been established so that even when the magnetic tape is transported at a speed 200 times that of the time of recording it is possible for its content to be read (see pp. 95 and 96 of the above-mentioned `Illustrated Digital Video Reader`).
In a digital recording and playback apparatus such as a digital VTR or a DAT recorder, a clock synchronized with recorded data is generated using a PLL. The PLL has a set range over which it operates even if the frequency of the inputted data fluctuates, and in consideration of stability of operation this is set to .+-.5% to .+-.10%. Consequently, when data is played back while the magnetic tape is being transported at a high speed, because the relative speed of the magnetic tape and the magnetic head deviates from that at the time of recording in correspondence with the increase in the tape speed, when the tape speed becomes high the frequency of the played-back data leaves the above-mentioned operating range of the PLL.
To avoid this problem, in for example a digital VTR, during cue/review operation, the practice of changing the free-run frequency of a VCO (Voltage-Controlled Oscillator) inside the PLL according to the operating mode (cue/review) and thereby enabling the PLL to remain locked even when the frequency of the inputted data fluctuates is known.
However, because in this method the free-run frequency is set to a fixed value depending on the mode, at times of transition, when the tape speed is changing, an error arises. Moreover, errors also arise due to dispersion among sets and ageing and so on. Although these errors can be tolerated during cue/review operation, when the magnetic tape transport speed is relatively low, at high speeds such as 200 times the recording speed they cannot be ignored.